# Photoelectric Effect Calculator

URL: https://speedycalculator.com/calculators/physics/photoelectric-effect/
Last updated: 2026-10-30

> The photoelectric effect calculator finds the maximum kinetic energy of electrons ejected from a metal by light, the stopping potential and the threshold wavelength, from the light's wavelength, frequency or photon energy and the metal's work function.

## Inputs

- Light given by
- Wavelength λ (nm, µm, mm, m, pm, Å)
- Frequency f (THz, PHz, Hz)
- Photon energy (eV, keV, MeV, J, zJ)
- Metal
- Work function φ (eV, keV, MeV, J, zJ)

## Results

- Photon energy
- Maximum kinetic energy
- Stopping potential
- Threshold wavelength
- Electrons emitted?

## Formula

```
K_max = h·f − φ,  V_stop = K_max/e,  λ_threshold = h·c/φ
```

## Explanation

Light knocks electrons out of metals only if each photon has enough energy – no matter how bright the light. Einstein explained this in 1905 using light quanta, winning his Nobel Prize.

### How to use the Photoelectric Effect Calculator

- **Light given by**
- **Wavelength λ**
- **Frequency f**
- **Photon energy**
- **Metal**
- **Work function φ**

Results update as you type, every field has its own unit menu, and everything is calculated in your browser.

### How it works

Choose how you describe the light and the metal (or a custom work function).

### Inputs explained

FieldWhat to enterLight given byChoose one: Wavelength, Frequency, Photon energyWavelength λUnits: nm, µm, mm, m, pm, ÅFrequency fUnits: THz, PHz, HzPhoton energyUnits: eV, keV, MeV, J, zJMetalChoose one: Caesium, Potassium, Sodium, Calcium …Work function φUnits: eV, keV, MeV, J, zJ

### What each result means

- **Maximum kinetic energy** = [Photon energy] - [phi]
- **Stopping potential** = max(0, [Photon energy] - [phi])
- **Threshold wavelength** = 6.62607015e-34×299792458÷([phi]×1.602176634e-19)

### Example values

How the main result changes when **Wavelength λ** changes and everything else stays at the example values above:

Wavelength λ (nm)Maximum kinetic energy (eV)1255.2687187.51.96252500.3094312.5-0.6825375-1.3438500-2.1703

## Worked example

Inputs — Light given by: Wavelength; Wavelength λ: 250 nm; Metal: Copper.

Results — Photon energy = 4.959368 eV; **Maximum kinetic energy = 0.309368 eV**; Stopping potential = 0.309368 V; Threshold wavelength = 266.63268 nm; Electrons emitted? = Yes.

## Key terms

- **Work function**: Energy needed to remove an electron from a solid.

## FAQ

**Why doesn't brighter red light eject electrons?**
Each photon still has too little energy.

**What is the work function?**
Minimum energy to free an electron from the surface.

**What is the stopping potential?**
The reverse voltage that just stops the fastest electrons.

**Which metal has the lowest work function?**
Caesium, about 2.1 eV.


## Sources

- [OpenStax – University Physics Volume 3](https://openstax.org/details/books/university-physics-volume-3)
- [NIST – Fundamental physical constants](https://physics.nist.gov/cuu/Constants/)